He highlighted figures showing the number of people prosecuted for drug trafficking in 2010-11 was 2941, with 2384 being found guilty, but by 2014-15, this had dropped to 2320 prosecutions, with 1890 being found guilty.

Mr McArthur believes these figures underline the need to look again at how authorities deal with those caught in possession of drugs for personal use, arguing that treating use as a health issue would free up police resources and enable enforcement activities to concentrate on supply.

He said: “This fall in the number of people convicted of trafficking drugs raises serious questions given recent reports that officers are being sent home from drug cases because of overtime costs.

“Does the reduction in convictions indicate real progress, or is it caused by diminishing police capacity?

“Criminal proceedings for drug trafficking are down 21 per cent in recent years. Meanwhile, the number of deaths we are seeing as a result of illegal drugs is at a record high.

“Police officers are under huge pressure and services are stretched. Under these circumstances we need to ask whether prosecuting users who need to be in treatment and education programmes, not in prison, is the best use of resources.

“Liberal Democrats want to see drug misuse treated as a health issue.

“This will help users get clean and give police freedom to prioritise tackling drug traffickers, ensuring they face tough criminal sanctions. The current system is simply not working.”